1. Field of the Invention
The present invention generally relates to a differential apparatus for vehicles, and particularly, it relates to a differential apparatus for vehicles including a differential gear mechanism and a difference limiting clutch.
2. Description of Relevant Art
FIG. 1 illustrates a conventional differential apparatus 201 disclosed by Japanese Patent Application Laid-Open Publication No. 46-8206.
The conventional differential apparatus 201 includes a differential gear mechanism 213 of a bevel gear type composed of a pinion shaft 205 fixed to a differential case 203 rotatable as an input member, a pinion gear 207 rotatably supported on the pinion shaft 205, and a pair of left and side gears 209, 211 as output members meshing with the pinion gear 207. The left and right side gears 209, 211 are axially movably splined on left and right axle shafts 215, 217, respectively.
The left and right axle shafts 215, 217 have left and right inner clutch members 219, 219 as pressure exerting elements axially movably splined thereon, respectively, which clutch members 219, 219 are frictionally engageable with left and right outer clutch members 221, 221 as pressure receiving elements fixed to the differential case 203, respectively. In other words, the left and right inner/outer clutch members 219/221 and 219/221 have their frictionally engaging surface parts cooperatively constituting left and right conical clutches 223, 223. The conical clutches 223, 223 are each adapted to be let in (left or right gear train) with a reaction force acting on the left or right inner clutch member 219 from the left or right side gear 209, 211 in a meshing state, thereby limiting a difference (in phase between left and right gear trains) at the differential apparatus 213.
In the differential apparatus 201, each conical clutch 223 is constituted by using the pressure-receiving clutch member 221 fixed to the differential case 203.
To this point, there is a conventional differential apparatus in which, as shown in FIG. 2, a difference limiting conical clutch 225 has its frictionally engageable elements directly formed on a side gear 229 and a differential case 227.
As illustrated in FIG. 2, the conical clutch 225 has at each point on a frictional engagement region thereof an inner frictional radius r1 on the gear 229 side and an outer frictional radius r2 on the case 227 side, which radii r1, r2 equal each other, thus evenly sharing frictional torque to be born.
A typical differential case is made of a spheroidal graphite cast iron (FCD), and typical side gears are made of a case hardened steel (SCM). They are both subjected to a surface hardening process by way of a carbo-nitriding or nitriding to have an enhanced anti-abrasive nature. Some differential cases have a structure with dispersed carbon (graphite) particles, with a slightly increased abrasion tendency.
To provide the differential case with an improved anti-abrasive nature, there is necessitated a higher surface hardness or a different material, with a significant increase in cost.
In the differential apparatus 201 also, there is observed a similar issue between each pressure-exerting inner clutch member 219 and a corresponding pressure-receiving outer clutch member 221.
Moreover, in this conventional apparatus 201, a space 231 is provided between the outer clutch member 221 and the differential case 203, leaving a fixed part 233 of the clutch member 221 alone to bear frictional torque of a corresponding conical clutch 223, thus needing a high strength at the fixed part 233, costing high.
Further, as the differential case 203 simply faces (without supporting) an outer side of the pressure-receiving clutch member 221 subjected at its inner side to the reaction force from a corresponding side gear 209, 211 in the meshing state, this clutch member 221 has a decreased anti-deforming tendency that might haste been improved by e.g. increasing its plate thickness, with an increased weight and an increased cost.